Allow chains to use current/factory presets/settings

Also gives builtin effects a mean to determine if batch processing
is active, IsBatchProcessing() returns true if so.

src/Menus.h

@@ -367,6 +367,8 @@ public:
    static const int kConfigured = 0x01;
    // Flag used to disable saving the state after processing.
    static const int kSkipState  = 0x02;
+   // Flag used to designate batch processing is active.
+   static const int kIsBatch  = 0x04;
 };
 
 bool OnEffect(const PluginID & ID, int flags = OnEffectFlags::kNone);